1. Field of the Invention
The present invention relates generally to an apparatus for supplying gas to a semiconductor process chamber. More particularly, the present invention relates to an apparatus for supplying thermally activated fluorine or oxidizing cleaning gas to clean a semiconductor process chamber, and a process for cleaning a process chamber with the thermally activated fluorine or oxidizing cleaning gas.
2. Description of the Prior Art
A primary step in the fabrication of semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of vapor precursors. A typical deposition process includes chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to form a thin film layer over the surface of the substrate being processed.
However, deposition occurs throughout the chamber, and not just on the substrate. The heaviest depositions occur in the hottest areas of the chamber, which is typically in the area of the substrate, but some deposition occurs in other areas, even fairly cool areas or areas not directly exposed to the vapor precursors, such as, chamber walls, windows, gas nozzles, tools, etc.
These depositions can cause a number of problems, such as, clogging fine holes in gas nozzles, disrupting an even flow of gas and affecting process uniformity, and clouding chamber windows affecting the ability to see into the chamber. In addition, they may form particulates, which can fall onto the substrate and cause a defect in the deposited layer or interfere with the mechanical operation of the deposition system.
To avoid such problems, the inside surface of the chamber is cleaned regularly to remove the unwanted deposition material from the chamber walls and similar areas of the processing chamber. Such cleaning procedures are commonly performed between deposition steps for every wafer or every n wafers. One type of procedure involves disassembling the chamber and cleaning each part using a solution or solvent, then drying and reassembling the system. This procedure is labor-intensive and time-consuming, reducing wafer fabrication line efficiency and increasing costs.
It is desirable to conduct the cleaning operations in-situ. Typical in-situ cleaning operations use, for example, nitrogen trifluoride (NF3), molecular fluorine (F2) and chlorine trifluoride (ClF3) as etchant gases in cleaning operations. In these typical cleaning operations, the gas flows to the process chamber. NF3 or F2 is typically activated by forming a low pressure plasma by supplying an radio frequency electrical field or magnetron method in the chamber or in a remote chamber before the chamber. ClF3 or F2 can be introduced directly to a heated chamber but, due to the reactivity of the gas, the chamber must be cooled from its operating condition to avoid damage to the components.
U.S. Pat. No. 6,242,347 to Vasudev et al. discloses another approach to cleaning a process chamber. The disclosed method includes a brief thermal cleaning step between wafers using chlorine as the halogen cleaning gas. The chlorine gas is admitted to the chamber at an elevated temperature of about 500 to 700xc2x0 F. The chlorine gas may be mixed with up to about 99.9% by volume of an inert diluent gas.
U.S. Pat. No. 6,375,756 to Ishibashi discloses a method for removing a film deposited inside a film-forming chamber. A hot element is disposed in a chamber and heated up to a temperature of 2000xc2x0 C. or higher after the chamber is exhausted. Thereafter, a oxidizing cleaning gas, which is decomposed and/or activated by the hot element to generate an activated species that converts the deposited film into gaseous substance is introduced into the chamber. The oxidizing cleaning gas may be fluorine, chlorine, nitrogen trifluoride, carbon tetrafluoride, hexafluoroethane, octafluoropropane, carbon tetrachloride, pentafluorochloroethane, trifluorochlorine, trifluorochloromethane, sulfur hexafluoride, or mixtures thereof.
There are several drawbacks associated with systems using heating elements to heat oxidizing cleaning gas. In U.S. Pat. No. 6,242,347, Cl2 gas is used which is not as reactive as F2 or ClF3 and is only suitable for deposits containing titanium. Since rapid removal of the deposits is desirable to reduce non-productive cleaning time, F2 and ClF3 would be more desirable cleaning agents but the heated chamber would be severely damaged at the temperatures used in this process. The less reactive Cl2 is therefore used.
Another drawback is that the oxidizing cleaning gas reacts with the element in U.S. Pat. No. 6,375,756. The temperature must be carefully controlled above 2000xc2x0 C. as stated in the patent to avoid reaction. As the element cools to run deposition processes, the elements is very vulnerable to attack. As a result, the element deteriorates and does not function as required. At the 2000xc2x0 C. temperature, metal atoms will evaporate from the filament and deposit in the chamber thus contaminating the chamber. Also, excessive heating of a process chamber by an element located within the chamber can cause damage to components and vacuum seals within the chamber. This is illustrated by the suggestion of coating the electrical connectors with platinum to protect them from attack. This is expensive and unreliable.
A process for thermally activating an oxidizing cleaning gas comprising the steps of: (a) reacting a oxidizing cleaning gas and a preheated inert gas to form a gaseous mixture containing radicals; and (b) passing the gaseous mixture to a reaction chamber, wherein the radicals react with one or more deposits contained within the reaction chamber to form a waste gas, such as SiF4, CF4 or TiF4.
The oxidizing cleaning gas is preferably selected from the group consisting of: fluorine, chlorine, XeF2, ClFx, BrFx, (where x=1,3,5), O2, O3, NF3, any fluorocarbon gas, other highly oxidizing or reactive gases, and any combinations thereof. The oxidizing cleaning gas is flowed to the mixing chamber at a flow rate between about 1 to 20 slpm.
The inert gas is preferably selected from the group consisting of: argon, nitrogen, helium, and any mixtures thereof. The inert gas is flowed to the mixing chamber at a flow rate between about 1 to about 20 slpm. The inert gas is preferably preheated to a temperature between about 400xc2x0 C. to about 650xc2x0 C.
The deposits found in the reaction chamber are typically silicon oxide, silicon nitride, polysilicon, tungsten silicide, titanium nitride, TaN, or combinations thereof, such that the waste gas is SiF4, CF4, WF6, TaF5 or TiF4.
The present invention also includes a system for thermal activation of a oxidizing cleaning gas comprising: a mixing chamber which is capable of reacting a oxidizing cleaning gas and a preheated inert gas to form a gaseous mixture having radicals; and a reaction chamber for use in semiconductor processing which is in gaseous communication with the mixing chamber, wherein the radicals react with one or more deposits contained in the reaction chamber to form a waste gas.
Preferably, the oxidizing cleaning gas is fed into the mixing chamber via a fluorine feed tube which has a diameter from between about xc2xc inch to about xc2xe inch.
The preheated inert gas is typically fed into the mixing chamber via an inert feed tube having a diameter from between about xc2xd inch to about 2 inch wherein the inert feed tube comprises a packed bed of thermally conductive material, e.g., a finely divided metal. The finely divided metal is preferably selected from the group consisting of: nickel, Hastelloy, stainless steel, and any combinations thereof. Copper and aluminum alloys may also be used if there is no contamination concerns for the particular process. The inert gas feed tube further comprises a heating means, wherein the heating means surrounds the inert feed tube. The heating means is selected from the group consisting of: electrical resistance heaters, radiant heater, gas fired combustion heaters, and any combinations thereof.
The reaction chamber is constructed from an inert material selected from the group consisting of: sapphire, dense aluminum oxide, nickel, Hastelloy and any combinations thereof. The reaction chamber comprises an outer tube and a liner inserted inside the outer tube. Preferably, the reaction chamber comprises a nickel outer tube and a sapphire inner tube. The inner tube would be sealed to the outer tube at a cool region at the opposite end from the outlet of the activated gas mixture.